Telephone system



May 26, 1942. A. LESTI 2,284,329

' TELEPHONE SYSTEM Filed Juiy 51, 1940 2 Sheets-Sheet, 1

KPH SS INVENTOR A. LEST/ A T TOR/V5 May 26, 1942. A. LESTI TELEPHONE SYSTEM Filed July 51, 1940 2 Sheets-Sheet 2 INVENTOR R www EG c mum A. LEST/ AT TORNEY Patented May 26, 1942 "EFEQE TELEPHONE SYSTEM Arnold Lesti, Glendale, Calif., assignorto American Telephone and Telegraph Company, a corporation of New York Application July 31, 1940, Serial No. 348,645 10 Claims. .(Cl.1'79--27 Systems have been devised heretofore in which.

the immediate release of all switches of the. connection takes place when the calling subscriber replaces his receiver and in which release ofj'the final or connector switch is effected at the end of a measured interval following the replacement of the called subscribers receiver provided the calling party i slow in hanging up his receiver. Moreover, it is common practice to employ the relay of the connector that responds to the called subscribers switchhook not only for the purpose of controlling the release circuits but also to effect a reversal in the direction of current flow in' the established connection for supervision or'for message register operation.

A feature of the present invention is an improvement in these prior systems which consists in including a thermostat in a connector switch having an element heated by electric current in a circuit established following the replacement of the called subscribers receiver when the calling subscribers receiver has not been replaced, causing the thermostat to close a contact after a regulated time interval for releasing the connector switch. A

Another and related feature consists in the use of a device common to a plurality of connectors cooperatively associated with the ther-' mostatic releasing unit to prevent interference between the operation of connectors used for intercepting calls and the operation and release of connectors associated with called subscribers stations.

Another and related feature consists in associating a distinctive signal with the calling subscribers line to signal the calling subscriber to replace the receiver after the automatic release of a connector by the called; subscriber.

Another and related feature consists inopening the conductors of a connector leading to the subscriber line terminals during the release of a connector, to prevent the association of a current source with these terminals if the calling subscriber has not replaced his receiver.

The foregoing and other features of the invention will be described more fully in the following detailed specification, which should be taken in conjunction with the accompanying drawings, and also in the appended claims.

Referring to the drawings, Fig. 1 shows abbreviated diagrammatic representations of a subscribers telephone Hil and dial I02, a line finder LF, and first and second selectors, SI and S2, all of the usual type in step-by-step offices including a diagrammatic showing of-the usual release magnets. There is also shown in detail a connector switch C includingan auxiliary releasing circuit the function of which is to efiect the release of connector C. At the right of Fig. 1 areshown connector terminals associated with conductors H38, H31, I08, I09, Hi1 and Ill leading to Fig. 2. To these terminals connector brushes H2, H3 and H4 have access.

In Fig. 2 there are shown two subscribers stations 263 and 2! 1, an intercepting operators cord circuit IC, which is adapted to answer intercepted calls and to complete these calls when required, and also a part of a cross-connecting frame 2M.

Assume that it is desired to discontinue service on the line of station 2 l1, and that it is necessary that incoming calls for this station be directed to anintercepting operator. For normal service the conductors 21 8, 2l9 and 283 for line 2|! are connected at frame 2! to conductors I09, H0

and'l l I, which lead to the terminals of connector C. The line is changed to intercept service by cross-connecting conductors I09, H0 and III to conductors 2|2, M3 and 282 by means of jumpers 215, ZIE and 28L respectively, at the same time opening. jumper connections with conductors ZIB, m. and 283 shown by dotted lines. At the left of Fig. 2 is shown another subscribers station 203, with dial 284, which is associated with line conductors I 66, lo! and H28 and the connector switch terminals of Fig. 1. For descriptive purposes it is assumed that the. subscribers line to station 253 is connected for regular, non-intercepted service. Its frame connections and line circuit are of the usual type found in step-bystep dial offices and are omitted here, the omissions being indicated by the dotted lines.

The finder LF and selectors SI and S2 may be of any suitable type, such as the Strowger switch, the operation and release of which are well known.

A detailed description of the operation of the system will now be given, first in connection with a call routed to station 203, for regular nonintercepted service, and secondly for a call to the intercepting operator who answers with-the intercepting cord IC.

Let it be assumed that the subscriber of line IOI desires to establish a connection with the station 203 and that the connection has been extended in the usual manner through line finder LF and selectors SI and S2 to the tip, ring and sleeve terminals of connector C. When this circuit is seized by the selector S2 a circuit is closed through the windings of relay I03 which may be traced from battery through the lower winding of relay I03, normally closed contacts 3 of relay "the units digits of the called number, i. e., for

I04, ring terminals and brushes of selectors SI; S2, and the line finder LF, thence over line con-.

ductor H5 and through subscribers telephone IOI and dial I02, over conductor IIB and'through tip terminals and brushes of line finder LF, and

selectors SI and'S2, normally closed contacts '2 of relay I04 and upper winding of relay I 03 to ground. Relay I03 operates which operates relay II'I through a circuit traceable from battery through the winding of relay II! to ground on the contact of relay I03. Relay I IT in operating connects ground on its contact 3 to the sleeve terminals and brushes ofselectors SI, S2 and line finder LF, thereby holding in the operated position the-selectors and line finder and guarding connector C from other hunting selector circuits.'

0n the first break of the contacts of dial I02 for the purpose of dialing the tens digits of the called number, relay I03 releases and closes a circuit from battery through'the windings of vertical magnet I and relay II9, lead I22, contact I' of the vertical off-normal contact assembly I2I, contact 2 ofjrelay II! to groundon the contacts of relay I 03. Relay I I1 is slow to release and does notrelease during the momentary open periods of the front contact of relay I 03, while responding tothe'pulses of dial I02. 'Relay l I9 and vertical magnet I20 are operated through the circuit hereinbefore traced. As soon as the shaft of the connector switch is moved from its normal position on its first vertical step, the vertical off-normal springs I2I operate and transfer the operating circuit for relay H9 and vertical magnet I20 from conductor I22, to conductor I23, thereby-placingthe windings of relay H9 and vertical magnet I20 in series through the make contact of relay-I I3, and contact 2 of the vertical oiT-normalspring combination I2I. This transfer from conductor I22 to I23 is made without interrupting the circuit, since the three upper springsof combination I 2| are of the makebefore-break type. After the contacts of dialI02 are closed again after the first break, relay I 03 reoperatesand againcloses the circuit through the winding of relay II'I, before this relay has hadv time to release, as hereinbefore explained. On the next open period of dial I02,,relay I 03 again releases and transmits a second ground pulse, through thecircuit of relay H9 and vertical magnet I 20. Relay H9 is slow to release and remains locked up over the open periods of the back contacts of relay I 03. The second ground pulse aforesaid causes the shaft of the switch to take another step upward. This action continues until all required pulses for the tens digits are transmitted by dial I02 and the connector brushes H2, H3 and H4 have reached the level containing the terminals of the line being called.

After the tens digit has been dialed and dial I02 is restored to normal, relay I03 remains operated," relay II9 releases, and the winding of vertical magnet. I20 is deenergized. When relay rotary stepping, relay I03 releases arid connects aground impulse to contact 2 of relay Ill and over the rotary stepping circuit just traced. Relay III remains operated during dial pulses, as in the case of vertical stepping. In response to said first ground impulse rotary magnet I24 will operate and cause the switch brushes II2, II 3 and H4 to rotate one step in a horizontal direction. Relay I25 operates to short-circuit the upper contacts of relay I to maintain the above circuit closed if relay I30 momentarily operates. Subsequent dial pulses cause rotary magnet I24 to step thefswitch around until the line 203 of the called subscriber is reached.

When dial I02 has-restored to normal the circuit'forrelay I25 and the rotary magnet I24 is opened since relay I 03 remainsoperated. Slow relay I25 does not release at once. Before connecting ringing current to this line a test is made to determine whether the line is busy or idle; If

' tion of the connector switch busy, ground will be found on the sleeve terminal connected to conductor I08, and will cause the operation of test relay I30 from" battery through it winding, contact 2 of relay I28, contact 2 of slow release'relay I 25, conductor I44, to ground on sleeve conductor I08 through brush II4. Relay I30 in operating opens the original circuit for rotary magnet I24 and when slow-release relay I25 finally releases the second circuit established'forrotary magnet I24 is opened and a holding circuit is established for relayI30. Relay I30 in operating connects the secondary winding of busy tone transformer I33 through its contacts 3, to the ring conductor I34 which indicates to the calling subscriber IOI that the called line .is busy. Relay I30 is locked up through a circuit traced from battery through the winding of relay I 30, contact 2 of relay I28, contact 2 of relay I25 released, contact 20f relay I30 to ground on sleeve conductor I35. Under this condition the calling subscriber will disconnect, causing the release of relays I03 and H1, thereby closing a circuit from battery through the winding of release magnet II8, contact 3 of VON combination I2I, contact 3 of relay I28, contact 2 of relay II! and contact of relay I03 to ground. Release magnet H8 is energized and causes the restorato normal, including VON springs I2I. Relay I30. which was locked to ground on sleeve conductor I35, releases since ground was removed by the opening of contact 3 of'relay I I I when this relay released. .The re-' moval of ground from conductor I 35 causes in the well-known manner the energization of release magnets I60, I6I and I62 of the preceding switches and the consequent release of these switches.

Let it be assumed now that the line 203 of the called subscriber is found idle. Under this condition battery will be found by sleeve brush II 4 on the terminal connected to sleeve conductor I08 through the winding of cut-01f relay 222. Under this condition relay I30 will not operate as hereinbefore described when the line 203 was found busy. After relay I25 has released upon the completion of rotary stepping, a circuit is closed for the operation of relay I28, which may be traced from aforesaid battery connection, on brush 4, through contact 2 of relay I25, lower winding of relay I28, contact 2 of relay I30, to ground on sleeve conductor I35. Relay I28, in operating looks through its upper winding and its contact 4 to ground on contact I of relay I". In operating relay I20. also connects tip conductor I38, through its contact I to ground on contacts. I of relay I33; opens the circuitof the winding of relay I30, by opening its contact 2; connects ground from pick-up interrupter I40 through its contact 5, contact I of relay I, contact 3 of relay. I39 to-battery through the winding of relay I4I. Relay I4I operates and locks through its contact I to ground on contact 3 of relay II'I. Relay I28 in operating also opens the lead to the rotary magnet I24 through its contacts 6; connects ring conductor I42 to ring conductor I43 through its contact 1, and joins sleeve conductor I35 to sleeve conductor I44, thereby grounding said conductor I44 for operating cut-off relay 222, and guarding the terminals of the line of subscriber 203 from seizure by another connector.

When relay I4I operates it closes a circuit for ringing the station 203. This circuit is traced from source of ringing current I41, which may comprise an interrupter connected with an alternating-current generator and with battery on different segments, through contact 2 of relay I4I, lower winding of relay I33, contact of relay I39, over conductor I43, contact I of relay I28, conductor I42, through connector brush H3 and associated contact, over line of subscriber 203, connector brush H2 and associated contact, conductor I38,contact I of relay I28, to ground on contact I of relay I39. The ringer (not shown) of station 233 is now actuated, but relay I39 does not operate until subscriber 203 answers by removing his receiver from the switchhook, thereby removing the ringer from the circuit and connecting a low impedance bridge across the line. Ringing tone is sent back to the calling subscriber over conductor I34 during the periods when ringing current is connected with station 203. The contacts of relay I39 are adjusted so that in operating a locking circuit is closed from battery through its upper winding and contact 2 to ground on contact I of relay II'I before the circuit through its lower winding is broken at either of its contacts I or 5. The operation of relay I39 disconnects ringing current from subscribers station 203. The locking circuit for relay I4I is also opened causing the release of the latter relay to disconnect the ringing source I41. In some instances the called subscriber such as the subscriber at station 203 may remove his receiver to make a call after a connector has bee-n connected to his line, but before relay I4I- has been operated by pick-up interrupter I40. To guard this condition a circuit is provided to operate relay I33 before ringing current is applied to this called station. This circuit may be traced from battery through contact 2 of relay I4I, lower winding of relay I33 and thence over the line. conductors as traced through station 203 to ground on contact I of relay I39. Under this condition the locking circuit for relay I39 is established through its upper winding in the same manner as previously described.

The conversational circuit between the calling and called subscribers is completed by relay I33 by closing through the tip conductors on its contact I, and the ring'conductors on its contact 5. Relay I33 in operating also completes the operating circuit for relay I04, which may be traced from battery through the upper winding of relay I04, over the tip conductors of connector C and the line of station 233,,through station 203 including dial 204, ring conductors of the line and of connector C to ground through the lower winding of relay I04. Relay I04 in operating reverses the direction of current over the line of calling station IOI, thereby causing the operation of an associated line message register (not shown) in the well-known manner. After the aforesaid reversal, battery through the lower winding of relay I03 is connected by contact 2 of relay I04 to the tip conductor, and ground through the upper winding of relay I03 by contact 3 of relay I04 to the ring conductor.

At the end of the conversation, when the calling subscriber disconnects, relays I03 and II1v release, removing ground from the upper locking windings of relays I33 and I28, which release. The release of relay I28 closes a circuit for operating release magnet I I8, which may be traced from battery through the winding of magnet I I8, contact 3 of VON combination I2I, contact 3 of relay I23, contact 2 of relay Ill, and the contact of relay I03 to ground. The operation of release magnet II3 restores the connector'switch to normal in the well-known manner. Also, the removal of ground from conductor I35 causes the operation of release magnets I60, IBI and I62 and the immediate release of the preceding switches LF, SI and S2.

A description will now be given of that feature of the system whereby the called subscriber by hanging up his receiver is enabled to effect a release of the connector C when the calling subscriber fails to disconnect and thus free his line for other calls. When the called subscriber at station 203 disconnects, relay I04 releases, but the calling party by keeping his receiver off the switchhook maintains the operative circuit for relay I03 and therefore relays II'I, I39 and I28 remain operated. With these relays operated and relay I04 released, an auxiliary release circuit is closed from battery through the winding of release magnet II8, contact 3 of VON combination I2I, heating coil I5I of thermostat I50, variable resistance I49, contact 4 of relay I33,

contact I of relay I04 to ground on contact I a of intercepting trunk relay 233. The current flowing in the circuit above traced through the winding of release magnet H9 and heating coil I5I is insufficient to operate the release magnet but is sufficient to heat the coil I5I associated with the bi-metal element I52 of the thermostat I59. The time period for heating the element I5I may be regulated by a movable contact I54 associated with the heating coil IEI or by a movable contact on variable resistance I49. After this regulated timeperiod has elapsed, the align ment of the bimetal element I52 is altered in such manner as to close contact I53. This eliminates the resistance of the heating coil I5I from the circuit traced through release magnet H8, which latter magnet now operates to-restore the connector to normal. The operation of the release magnet opens its contacts I and 2 to prevent battery and ground clicks as the brushes H2 and H3 pass over line terminals While releasing. This battery and ground is associated with brushes H2 and II 3 through the and I28 since'at this time neither relay I 39 nor I28 have released It will be remembered that the latter relays. are locked 'to ground on con tact- I of relay -II'I through contact -2 and the upper winding of relay I39 to battery and through contact 4 and the upper winding of relay I28 to battery. When the connector has completely restored to normal, the vertical offnormal contact combination I2I restores to normal which establishes atone circuit for an nouncing to the 'calling'subscrib'er that his receiver should be returned to the switchhook. This tone circuit may be traced through the secondary winding of tone coil I33, contact 4 of the vertical off-normal combination I2I to conductor I42, contact I of relay I28, contact 5 of relay I29 and thence'over the ring conductor to the subscriber station I M The subscriber. hearing this tone simulating a busy connection, replaces his receiver upon the switchhook. This action restores relay I03 to normal which-opens the operating circuit for relay II1 which is slow to release, and restores to normal after a short duration'of time; The release of relay II'I opens the locking circuit for relays I39 and I28 which release, placing the connector in a normally-m stored condition. The preceding switches, LF, SI and S2 are released as previously described. It should be noted that'the'eme rgencytone circuit is only established when the switch is in its normal position since whenever the switch is active or associated with other terminals, contact 4 of the contact combination I2I is opened. 1 The thermostat I50 is individual to each connector and consequently a connector which is released under the control of this thermostat will not interfere with the normal release circuit of other connectors in a connector group. As will be remembered, the normal releasing circuit for connectors of this group does not extend to the common ground on contact I of relay 286 but is energized over a circuit extending manner previously described. It is ordinarily possible to use one intercepting operators trunk fora plurality of disconnected lines which formerly were reached through the connectors of a group and therefore the intercepting operators trunk, comprising conductors 2I2, 2I3 and 282, jack 20I and relay 286, may be connected to all of the disconnected line terminals associated with the connector group having connector C,

through normal contact 3 of relay I28, normal contact 2 of relay II! to ground on the normal contact of relay I03. As previously stated, the,

only occasion for the energization of the emergency or auxiliary releasing device is when the calling party does not replace the receiver on the switchhook for a time period after the called I party replaces his receiver which gives the element I5I time to be heated and close the asso-' ciated contact I53 for energizing the release magnet. a

A group of connectors such as connector C, Fig. 1, may have a number of lines which were associated with switch terminals, but which, through change of address of the subscriber or for other reasons, have been disconnected. The switch terminals'for all lines are carried to crossconnecting frames where jumpers are used for flexibility in connecting and disconnecting subscribers lines. Very often a line which is not in service is called by persons familiar with the line number but unaware that the line is no longer in use. Such calls are automatically routed to an intercepting operator who gives the calling party information'regarding the change. Calls of this character are not registered against the calling party' and consequently there is a diiference in the operation of a connector associated with a trunk to an intercepting operators position such as IC and a connector associated with a called subscriber such as 203 who in answering the call operates the connector in the I the terminals of line Fig. 1, therein and a plurality of other like connector-s. When there is more than one intercepting trunk for a connector group relay 286 may be made cormnon to these trunks and the connectors of thefconnector group or a plurality of relays maybe made common to the connector group by the use of a chain circuit throughthe contacts I of relays such as 286 to a ground on one relay armature.

The'operation of the system has been described for a regular, non-intercepted call between subscribers. The system' will now be described in its operationfor an intercepted call. Assume for this purpose that the calling subscriber at station IOI wishes to be connected to subscribers line 2I I, Whose telephone, as hereinbefore stated, has been removed from service by disconnecting conductors I09 and H0 on frame 2I4 from line conductors 2| 8, and2I9, and by cross-connecting said conductors I09 and II 0 by jumpers 2I5 and H6 to conductors 2I2 and 2I3 leading to jack 20I at an intercepting operators position. Also the line relay is disconnected, and the sleeve conductor 1 I I 'is disconnected from cut-01f relay 220and connected by jiunper 20I to sleeve conductor 282 of the intercepting trunk 2I22I3. Let it be further assumed that a connection has been made in the usual manner by connector brushes H2, H3, II 4;with terminals connected to conductors I09, IIOLand III of'line 2I'I which is now connected to an intercepting trunk. The descriptionof theoperation for establishing the connection with conductors I05, I01 and I08 is sufficient to explain the connection with conductors I09, I I0 and II I, Whenthe connector switch engages I09, IIO, III, relay I28-operates in the manner already described, the current for operating the relay being furnished in thisins tance from battery through the left winding of relay286 and thence I28 as previously traced. Intercepting trunk relay 280 is operated in the circuit traced which removes ground from the auxiliary connector release circuit operated by thermostat I50 for reasons-which will be apparent in the following description. a

Ringing current transmitted over conductors 2I2' and 2I3 through the lower winding of relay I'39.in,the manner previously described causes the operation of a line signal (not shown) associated with jack 20I. The intercepting operator in response inserts plug'223 into jack 20I, thereby closing a circuit for operating relay 224, over a circuit that may be'traced from battery on con-' over conductors 282, 28I and III through the lower winding of relay through its lower winding to trip the ringing current in the manner described hereinbefore in connection with the call to station 203. The circuit for operating relay I39 may be traced from ground on contact I of relay 226, contact 3 of relay 221, resistance 229, contact 2 of relay 226, ring conductors of plug 223 and jack 20I, conductor 2I3, jumper 2I5, conductor IEO, brush H3, conductors I42 and I43 and associated operated contact I of relay I28, contact and winding of relay I39, contact 2 of relay I4I to the source of ringing current I4'I. Relay 221 in operating locks to ground on the sleeve of jack 2!", through its contact 2 and operates relay 238 through an obvious circuit. Relay 230 in operating, operates through an obvious circuit relay 225, which disconnects ground from its contact I and the winding of relay 224 from its contact 2. Relay 224 releases. Relay 225 in operating establishes a conversational circuit over the ring conductors of cord circuit 10, connects ground to conductor 23I through the upper contacts of key 238 and connects a high impedance and high resistance bridge across the tip and ring conductors of cord circuit'IC and the tip and ring conductors of the associated connector, said bridge including retardation coil 235, and relays 232. and 235 all in series. In multiple with the series connection of the'windings of relays 232 and 236 is a resistance 236. The windings of relay Hi4 of the connector are thus placed in series with the above bridge circuit. Relay 232 operates from battery and ground in series with the windings of relay I04 over the tip and ring conductors of cord circuit IC, through the operated contacts of relay 225, thence over tip and ring conductors of the connector C, which are closed through by operated contacts on relays I28 and I39, Because of the high resistance in the bridge circuit traced, connector relay I04 does not operate. Accordingly there is no reversal of current over the tip and ring conductors extending towards the station of calling subscriber IDI, thereby avoiding the operation of the line register which, of course, should not operate on this call to an intercepting operator. Relay 232 inoperating, disconnects the windings of relay 225 from contacts 3 of relay 233. Consequently relay 225 does not operate when ground is connected to conductor 23I by the aforesaid operation of relay 226. Polarized relay 236 does not operate in series with relay 232 for this type of call as the current flow through its winding is in the direction opposing operation. The intercepting operator now operates the listening key 239 and thereby connects the operators telephone (not shown) over conductors 290 and 29I to the tip and ring conductors of the cord circuit IC. The operator converses with the calling subscriber IIII and if desired the connection may be extended over another line (not shown) which terminates on jack 292.

. Consideration may now be given to a number of 7 requirements in the operating conditions of a plurality of connectors simultaneously functioning in different manners in the same connector group. For example, a number of connectors may be connected to subscriber stations such as 203 and released therefrom in the normal manner by the disconnection of the calling subscriber and the energization of the normal release circuit as traced. Another connector in this group may be held by the calling subscriber after the called subscriber has disconnected, and thus the called line is made free by the release of relay I04 and the energization of the auxiliary re.-

lease circuit through the thermostat heating coil I5I to ground on the intercepting trunk relay 286 common to the connectors of the group. Also at times which are usually infrequent a connector of this group is associated with an intercepting operators position over an intercepting trunk. It was noted in the description of a call to an intercepting operator that relay I04 in the connector is not operated, which prevents operation of the calling line message register. The connector relays when functioning on an intercepted call are therefore in the same condition in so far as operated and released positions are concerned as they are after a call has been made to a subscriber such as 203 and this subscriber has disconnected but the calling subscriber has not disconnected. In order to provide the advantages of freeing the called subscribers line when held by the calling subscriber, with a minimum amount of equipment added to connectors of the wellknown and standard type, and prevent interference between functions of the connectors of a group, the intercepting trunk, when seized, has been arranged to disconnect the ground from the auxiliary release circuits of all connectors in the connector group. This prevents the energization of the auxiliary release circuit in the con nector associated with the intercepting operators position. At such times the auxiliary release circuit in other connectors of the group is not operative but is again operative upon the disconnection of the intercepting trunk circuit. The time consumed in answering an'intercepted call is of short duration, and therefore if one connector ,is connected with an intercepting trunk when the auxiliary release circuit is closed in another connector, the time consumed by the intercepted call, is negligible when added to the time consumed in heating the thermostat element I5I for energizing the auxiliary releasing circuit in another connector circuit after relay 286 has released.

What is claimed is:

1. In an automatic switching telephone system, subscribers lines, a connector switch for completing connections between calling and called subscribers lines under the control of the calling subscriber, a device for releasing said connector switch, a thermostat individual to said connector having a heating coil and acontact operable in a regulated time period, a releasing circuit for energizing said device to release said connector established bythe closing of said thermostat contact, and means only under the joint control of the calling subscriber and the called,

subscriber for heating said coil to close said thermostat contact.

connector having a heating coil and a contact operable ina regulated time period by electrical current, a releasing circuit vfor energizing said device to release said connector established by the closing of said thermostat contact, and means efiective on said first relay operated and said second relay released for heating said coil to close said thermostat contact.

3. In an automatic switching telephone system, subscribers stations, a connector switch for completing connections between calling and called subscribers stations under the control of the calling subscriber, a relay operated and released under the control of the calling subscriber, a second relay operated and released under the control of the called subscriber, a connector switch releasing device, a; releasing circuit for energizing said device, means'under the control of said first relay released for establishing said releasing circuit, an auxiliary releasing circuit for energizing said device including a thermostat having a heating coil and a contact operable in a regulated time period, means under the control of said first relay operated and said second relay released for establishing said auxiliary release circuit for heating said element to cause the closure of said contact foroperating said release device, and means responsive to establishing either of said releasing circuits for disconnecting said connector switch from the called subscriber's station.

4..In an automatic switching telephone system, subscribers stations, a connector switch for completing connections between calling and called subscribers stations under the control of the calling subscriber, talking conductors established by the operation of said connector switch, a relay operated and released under theicontrol of the calling subscriber, a second relay operated and released under the control of the called subscriber, a connector switch releasing magnet, a thermostat having'a heating coil and a contact operated in a regulated time period, a releasing circuit for energizing said magnet established by the closing of said thermostat contact, means under the control of said first relay operated and said second relay released for establishing said releasing circuit, means responsive to the estab lishing of said releasing circuit for disconnecting said connector switch from the called subscribers station, and means-operated by said release magnet for opening the connector talking conductors before said switch and conductors are disconnected from the called station.-

5. In' an,automatic switching telephone system, subscribers lines, a connector switch for completing connectionsbetwen calling and called subscribers lines under the control of the calling subscriber, a relay operated and released under the control of the calling subscriber, a relay operated and released under the control of the called subscriber, a releasingdevice for said connector switch, a thermostat having a heating coil and a contact operable in a regulated time period by electrical current, 'a releasing circuit tablished by the closing of said thermostat confor energizing said device established by the closing of said thermostat contact, means effective on said first relay operated and said second relay released for heating said coil" to close said thermostat contact, and-means responsive to the release of said connector switch for connecting a distinctive signal to said calling subscriber's line,

6. In an automatic switching "telephone system, subscribers lines, intercepting trunks, a plurality of connector switches for completing connections between calling and called subscribers. lines and between calling subscribers lines and intercepting trunks, each connector including a thermostat having a heating coil and a contact operable by electrical currentin a regulated time period, a relay operated and released under the control of the calling subscriber, a second relay operated and released under'the control of the called subscriber, a switchreleasing device, a

releasing circuit for energizing said device estact, means effective on said first relay operated and said'second relay released for establishing said releasing circuit to close said contact, means responsive to the operation of said magnet for disconnecting said connector switch from a called subscribers line, and means in said intercepting trunk circuit operable when seizedby one of said connectors for cooperating with said plurality of connector switches for disabling said releasing circuit. E V V c c 7. In an automatic switching telephonesystern, a plurality of connector switches, subscrib ers lines incoming to said connector switches, subscribers lines outgoing from said connectcr switch terminal banks, intercepting trunks associated with certain terminals oi said terminal banks common to said plurality of connector switches, a thermostat having a heating coil and a contact operated in a regulated time period; individual to each connector switch, a releasing devicefor said connectorswitch, a relay operated and released under the control of the callingsubscriber, a second relay operated and released under the control of the calledsubscribena releasing circuit for energizing said device established by the closing of'saidthermostat contact, means effective on said first relay operated and said second relay released for heating said coil to close said thermostat contact, means respon-; sive to the operation of said device for disco n; necting one of said connector switches from a called subscribers line, and-arelay in said com-; mon intercepting trunk circuit operable in response to the seizure of said trunk by a connector for cooperating with said plurality of connector switches to disable said releasing circuit.

a. In an automatic switching telephonejsystem, subscribers lines, a connector'switch for; completing connections between calling and;

called subscriber lines under the control 01 the calling subscriber, a device having an electrically,

operable magnet for releasing said switch, fa

thermostat having a bimetal element, a heat-.

ing coil and a contact operablein a regulated time-period, a releasing circuit extendingin series through said heating coil and said release magnet for heating --said coil to alter the align-.1 ment of said-birnetal'element which closessaid contact to-shunt the heating coil and causeran, increase of current through said magnetfor energizing said magnet, and means under the joint, control of the calling subscriber and the called subscriber for establishing said releasing circuit, to operate said device andv release said connector switch.

9 In an automatic switchingjtelephone sys-j tern, subscriberslines, a; connector switch for completing connections between calling and; calledsubscribers lines under the control 101 the' calling subscriber, a relay operated and released under the control-of the calling subscriber, a relay operated and released; under-the control: of the called subscriber; a magnet forrreleasingsaid connector switch, an electrically'operable; device having a winding and 'acontact individual to said connector switch; an electrical:

circuit extending through said device winding,

and said magnet for energizing said device to close its contact for shunting saidto operate said magnet for releasing said connector,

switch and means effective on said first relay operated and'said second relay released for establishing said circuit.-

- 10. In an automatic switching telephone sy'si tem, subscribers lines, a connector switch for completing connections between calling and called subscribers lines under the control of the calling subscriber, a relay operated and released under the control of the calling subscriber, a relay operated and released under the control of the called subscriber, a device for releasing said connector switch, a thermostat having a heating coil and a contact operable by electrical current, 

